Recently, ink-jet recording system has been applied in various fields of printing works such as photograph imaging, various types of printings, markings and a specific printing such as a color filter because it enable to form an image easily and with low cost.
Ink-jet ink used for the ink-jet recording includes various types of ink such as an aqueous ink containing water as a principal solvent, an oil-based ink principally containing a non-volatile solvent at room temperature and substantially containing no water, a non-aqueous ink principally containing a solvent volatile at room temperature and substantially containing no water, a hot-melt ink which is solid at room temperature and thermally melted for printing and an active light curable ink capable of curing by active rays such as light, which are selected in accordance with the use.
Besides, a recording medium made from plastics such as polyvinyl chloride and polyethylene is used for outdoor notice board which is required to have a weather resistance for a long period and ability of contacting with a curved surface is used, particularly a medium made from sofi polyvinyl chloride is used in wide field of use. The ink-jet recording method is applied as a method suitable for making small amount and diverse kinds of printing matters since plate making is not necessary and the time for finishing is short in such system, though many methods are applied for printing an image on the polyvinyl chloride.
Hitherto, the non-aqueous ink containing cyclohexanone as the principal solvent is used on the occasion of printing on the soil polyvinyl chloride recording medium, for example, an ink-jet ink containing cyclohexanone is disclosed (cf. Patent Document 1). Cyclohexanone has high dissolving ability for soft polyvinyl chloride so that the pigment contained in the ink is come into soft polyvinyl chloride. Therefore, high abrasion resistance and high glossiness of the printed matter can be obtained. However, cyclohexanone is regulated as the First Class Organic Solvent and causes a problem of safety and a local exhaust system is necessary on the occasion of handling the ink-jet ink containing cyclohexanone. Further, organic solvents such as cyclohexanone has potent odor and has issues of long-lasting odor of a printed matter as well as being burden to workers.
In contrast to that, non-aqueous ink containing no cyclohexanone is developed and marketed. For example, non-aqueous inks containing a water soluble organic solvent such as N-methylpyrrolidone and lactone as the solvent capable of dissolving polyvinyl chloride in place of cyclohexanone causing the above problems are disclosed, cf. Patent Documents 2 and 3. Moreover, a non-aqueous ink containing a fixing resin such as a vinyl chloride-vinyl acetate copolymer and an acryl resin for improving the fastness of the image such as abrasion resistance is disclosed, cf. Patent Documents 4 and 5. An ink-jet ink which is inhibited some degree in the odor thereof and has the abrasion resistivity of image formed thereby on polyvinyl chloride medium can be obtained by such constitution.
However, in the case of using above water soluble organic solvent, it was found that an abrasion resistance or a water resistance of a printed image was deteriorated after long period storage and also a gloss of printed image was deteriorated, even if using an ink caused no defect immediately after an ink preparation. Further it was found that in some cases, unstable ejection from an inkjet head occurs and results in a misfire during printing. Moreover, it was found that the operational abnormality of the ink-jet printing head is caused in long-term use in some cases using such organic solvent. Accordingly, any non-aqueous ink-jet ink is not obtained yet, which has no problem of the safeness and odor and sufficient suitability for printing onto polyvinyl chloride and can be used for a long period.
Patent Document 1: Japanese translation of PCT international application 2002-526631
Patent Document 2: Unexamined Japanese Patent Application (hereinafter, refers to as JP-A) No. 2005-15672
Patent Document 3: JP-A 2005-60716
Patent Document 4: JP-A 2005-36199
Patent Document 5: WO 2004/007626